1. Field of the Invention
The present invention generally relates to a method and an apparatus for determining whether a vehicle has been regeneratively braked and for frictionally braking the vehicle in the event that the vehicle has not been regeneratively braked and to a vehicle which incorporates the method and apparatus and more particularly, to a method and apparatus which measures and/or senses the speed and deceleration of a vehicle after a regenerative braking assembly has been activated, effective to determine whether the vehicle has been regeneratively braked and, based upon the measured or sensed speed, activates a frictional brake assembly, effective to brake the vehicle.
2. Background of the Invention
A vehicle may be braked or selectively decelerated or slowed by the use of several techniques or strategies. For example, a hybrid type vehicle may be regeneratively braked by selectively coupling the torque emanating from the transmission or powertrain assembly to an energy storage device (e.g., a storage battery or hydraulic accumulator), thereby conserving energy while slowing or decelerating the vehicle. While such regeneration does desirably slow a vehicle's velocity or speed, it does not typically provide sufficient deceleration to actually stop the vehicle. Hence, these regenerative braking strategies must normally be used in combination with traditional braking strategies which require the use of a frictional brake assembly on each of the wheels. Particularly, a frictional brake assembly selectively engages the wheel on which it is operatively disposed and, in this manner, these frictional brake assemblies selectively and cooperatively decelerate and stop a vehicle.
There exist a number of unique strategies which utilize such frictional braking assemblies and which seek to dynamically distribute the amount of braking between braking assemblies located at the rear of the vehicle (i.e., behind the driver) and the front of the vehicle in order to maintain overall vehicular stability. Typically, the vehicle is initially regeneratively braked in order to maximize the amount of energy which may be regeneratively stored and concomitantly decrease the use of the frictional brakes which wear over time and must be replaced or serviced.
It is desirable to confirm whether regenerative deceleration of the vehicle has occurred and/or to confirm that the regenerative braking system is operable in order to avoid a relatively sudden application of the frictional brakes which is necessary in order to achieve the desired vehicular braking. Particularly, such a sudden application of the frictional brakes both reduces the operating life of these brakes, provides discomfort and annoyance to the passengers of the vehicle, and oftentimes prevents a desired brake distribution to occur. The present method and apparatus provides this confirmation benefit and provides a strategy which eliminates or reduces the need to suddenly and fictionally brake a vehicle due to an inability of the regenerative braking system to supply the desired braking.
The current state of the art is generally shown by U.S. Pat. Nos. 5,378,053, and 5,839,800. The '053 patent discloses a regenerative braking system which alerts the vehicle's driver that a system fault has occurred. The '800 patent uses an accelerometer to detect operation of a regenerative braking system. However, neither the '053 patent nor the '800 patent teaches that operation of a regenerative braking system should be monitored or shadowed by a redundant system, so as to improve the reliability of the overall regenerative braking system.